The Care of Young Trees: Elm and Other Deciduous Trees

Contributed by Honey Sharp Lippmann, Master Gardener

”Young trees are like children”, Dr. Bruce Fraederick announced at his seminar, “The Pruning and Training of Elms from Nursery to Maturity”. Organized by Elm Watch and the FFA (formerly, Future Farmers of America), it was held at the Housatonic Valley Regional High School in late September 2003. “Until trees are twenty years old, they require lots of attention. It’s in the first ten years that they need the most; after twenty, they’re independent,” he explained. (I would add that trees are also like old people: they’ll need attention again one day, but then, we probably won’t be around.)

Who knew that young trees would need care? If you just plant them properly (never too deeply) and water them, won’t they simply thrive? Fraederick, the vice-president of research at The Bartlett Tree Laboratory, brought up a number of thought-provoking questions as well as practical guidelines on this question.

In pointing out how trees basically manage fine in the woods, he highlighted the contrasts between natural and manmade environments. It is in the latter, where a tree, in its landscaped situation with greater exposure to the sun and less competition from neighboring trees, will require pruning. In contrast, with reduced or filtered light, a forest tree’s principal leader will be encouraged to grow vertically towards the source of light. (Could this argument be used for placing children in a crowded classroom or better yet, for leaving them in the wild?)

In focusing on the ongoing pruning program young trees require, Fraederick referred not only to elms but to other tree species as well. Not all trees are the same. Most evergreens do fine without pruning, unless the goal is small size or the creation of a hedge. And, among deciduous trees, tulip trees, oaks, and beeches, all show a strong apical dominance, i.e. a good leader. And, in the case of birch trees, their “destiny” is to maintain multiple stems. However, deciduous trees such as maples and elms are another matter. To complicate matters further, not all elms are the same. Valley Forge elms, with their explosive growth in all directions, need far more pruning than Princeton elms. But more about that later.

As Fraederick so succinctly explained, the reasons to prune are not only esthetic but also for the health of the tree. The first apparent reason to prune young elms is to enable them to develop their optimum form: that wonderful umbrella shape we all desire. The more fundamental reason is to avoid a potential weakness later on caused by the growth of multiple stems or leaders. Not only elms but maples have this tendency, causing stress and ultimate breakage of the branches. Side leaders – major branches taking over and eclipsing the vertical leader – a potential issue with these species, are no longer a problem when pruned at a young age.

How does one go about this? Instead of removing entire side branches that are beginning to dominate the tree in its early years, Fraederick demonstrated a technique more similar to what occurs in nature – a type of natural selection process. He advocates slowly paring down the tree by selectively cutting the dominating side branches by only a third. As he explained, leaves are necessary for the production of the photosynthesis necessary for the tree’s health and growth. Removing a few smaller side branches is acceptable, however, to encourage the main leader.

The concept is that the dominate leader will prevail . Cutting back those few select side branches will encourage what Fraederick called “subordination”. This will prevent later problems during major storms. And, side branches cut back may eventually simply fall off as they are eclipsed by larger branches.

Valley Forge elm, a popular, disease-resistant elm, unfortunately has, as he put it, “very aggressive branch growth”. Such trees definitely need training. In his demonstration with young 10’ tall elms at the high school nursery, Fraederick pointed out how the goal is symmetry for branches all around. He generally delays in removing the lower branches, mentioning how this can be done later. Finally, he also stressed how maintaining a visible root collar is essential. Don’t pile mulch around the tree; it only leads to disease.

With the 20 to 25 elm cultivars and hybrids one can select from today, it is worthwhile researching how much care they will require in their early years. Wouldn’t it be nice to know this about our children? But then, again, surprises are what make it worthwhile.